Compared with conventional diodes, Zener diodes have a lower breakdown voltage (also called Zener voltage), which is typically about 6 V. The low breakdown voltage of the Zener diode is the result of the heavily doped PN junction that produces the Zener breakdown through the tunneling mechanism. Within the heavily doped PN junction, under a reverse bias condition the conduction band and the valence band are very close so that electrons can tunnel directly from the p-region valence band to the n-region conduction band.
Zener diodes are semiconductor devices having a high resistance until the critical reverse breakdown voltage. At the critical breakdown point, the reverse resistance is decreased to a small value, the current increases while the voltage remains constant. Zener diodes are grouped according to their breakdown voltages. Because of the accurately determined and constant breakdown voltage, Zener diodes are typically used as voltage regulators or voltage reference elements. The typical application of Zener diodes is the clipper circuit where two Zener diodes have their cathodes connected to each other and their anodes connected across the input terminals of a circuit to limit the positive and negative voltage amplitudes of the circuit. FIG. 1A shows a clipper circuit having two Zener diodes Zener1 and Zener2 having their cathodes connected to each other and their anodes connected to the output terminals. FIG. 1B shows the voltage waveform where the negative amplitude is clipped by Zener1 and the positive amplitude is clipped by Zener2. The clipper circuit not only can be used for signal shaping, but also as overvoltage protection to prevent voltage spikes from occurring to electronic devices or components.
In order to predict the Zener diode performance and reliability in an application environment, the behavior of Zener diodes needs to be simulated. However, conventional Zener diode models do not accurately describe the reverse bias current and voltage of the Zener diode.